Generally used to refer to a Vietnamese male with the following specific appearance characteristics; long-sleeve thermal (black/white in color), a short sleeved polo shirt over the thermal (black/white/grey in color), designer brand jeans and/or black/grey Dickies, Vans/Converse (Chuck Taylors) shoes, exposed tattoos on either one or both arms (usually 3/4 sleeve to full sleeves. Common tattoos are Koi fishes, oriental dragons, chinese calligraphy, tiger, etc...) and a NewEra fitted cap worn a specific way as to where the cap sits/tilts lower towards the front on the head (usually on/covering the eyebrows) and higher on the upper back of the head (similar to how drill sergeants/state troopers wear their campaign hats).

The word dumani is singular, referring to only one person. Dumanis is plural. The word consists of "Du ma", a very vulgar Vietnamese cuss word.
Dumanis are NOT to be confused with Vietnamese gangsters, Dumanis typically look/act "hard/gangster" in appearance but will never do anything or fight anyone by themselves. a Dumani likes to "mean mug"/stare at other Dumanis in a taunting manner. Dumanis are mostly seen in Northen California but also seen in areas with a high Vietnamese population such as Orange County, Los Angeles, Houston, etc...

Any person(s) with the similar characteristics that is any other race/ethnicity other than Vietnamese would be called a "their race" Dumani-lookalike (i.e.: Chinese Dumani-lookalike, White Dumani-lookalike, etc...)

Look at this Dumani fool right here, I think he has a staring problem...